At helicopters a phenomenon is common that makes the rotor blades move up and down in their vertical direction, i.e. in the vertical direction in relation to the helicopter. This movement is called “flapping” and is an important factor in the helicopter's behavior in the air during flight. Seizing or malfunctioning flapping hinges can affect the helicopter's function and dynamics in a negative way, which may lead, in the worst case, to a sudden failure or breakdown.
It is therefore desirable to monitor e.g. at what pitch the rotor blades are “flapping”. Monitoring the vital parts of a helicopter, for example the flapping hinges, may result in a less risk of a serious failure in the long run. It is also possible to get a better understanding of when maintenance is really necessary and when it is necessary to change vital parts in the helicopter. This may result in longer running time for expensive parts before they need to be replaced instead of having a fixed replacement interval, when fully functional parts are exchanged unnecessarily.
The present invention is based on the design of a device or a system including linear position transducers (LDT) by which it is possible to monitor and calculate when and how much the, for instance two, rotor blades are “flapping” upwards. A rotor blade is “flapping” with about the same frequency as the rotor speed, allowing the signal to come out from the system as a sine curve. The flapping frequency depends on the rotor configuration and some parameters for example the flapping hinge offset from the rotor center of rotation
There have previously been several attempts to design systems for detecting the flapping angle α of the rotors in a helicopter.
U.S. Pat. No. 2,620,888 illustrates for example a system that indicates and corrects the unbalance in the lifting force of the rotors of a helicopter. The document describes a mechanism that detects differences in the flapping between the rotors, and then compensates the flapping behavior by means of a hydraulic system. This mechanism does not for instance include any electronic or linear sensors.
U.S. Pat. No. 2,936,836 illustrates a rotor blade tracking mechanism for lifting rotors of a helicopter and the purpose of the invention is to indicate and correct for lifting differences between the rotors in order to minimize undesirable vibrations. The document describes a system that detects unbalance in the flapping behavior between the rotors.
This is based on that the angle between the rotors is changed and the system makes use of that the flapping hinges generate sinus wave formed motions.
Both these documents describe systems for compensating for differences in flapping and for the purpose of reducing vibration levels. The wear of a component is not monitored or detected in itself.
WO20120953325 describes a function-monitored guidance system, a high-lift system, with a monitoring device providing operating state determination function for determining overshoots of stored threshold values. The invention illustrates surveillance of components in order to discover wear, primarily at interceptor aircraft in which sensors measure the mechanical properties such as load states of a component like a flapper point or a bearing and compare these values with desired predetermined values. The sensors measures for example vibrations, acceleration or tension.